The present invention generally relates to intermittent dispensing processes and apparatus involving liquid materials such as hot melt adhesives, cold glues and sealants. More particularly, the present invention relates to a dispensing head or nozzle which prevents drooling or dripping of such adhesives or glues during the shut off period upon completion of a dispensing operation.
In an intermittent dispensing operation of, for example, hot melt adhesives or cold glues, the shut off periods between the dispensing operations present opportunity for accumulated adhesive or glue in the dispensing head or nozzle to drip or drool from the dispensing head. Often, this dispenses adhesive or glue in unwanted locations such as, for example, in undesirable locations on the substrate or on the conveyor system which transports the substrate. Certain solutions to this problem have been presented in the prior art. One solution is contained in U.S. Pat. No. 3,315,899 which discloses a dispensing body having a piston which is raised into the body upon shut off of the nozzle to decrease the pressure in a chamber within the nozzle. This decrease in pressure pulls hot melt at the nozzle outlet back into the chamber to prevent drooling or dripping of adhesive after shut off. The drawback with this design, however, is that the adhesive drawn back into the chamber must be expelled at the beginning of the next dispensing cycle. Also, dripping will still occur with this design if the discharge orifice is large enough and/or depending on the physical properties of the dispensed liquid.
U.S. Pat. No. 3,841,567 discloses a dispensing nozzle having a minimum volume cavity above the nozzle supply passage and a nozzle tip having a minimal lip area which, taken together, prevent drooling or dripping of material from the nozzle tip after shut off. This solution to the drooling problem is unacceptable in dispensing applications requiring nozzles having large dispensing passageways or in situations where there is otherwise a need to shape or control the stream of material exiting the nozzle.
U.S. Pat. No. 4,408,562 discloses an air wipe method and apparatus for preventing drooling or dripping of material upon shut off of a coating dispenser. More specifically, a pressurized air supply is positioned adjacent to the nozzle outlet to direct a pressurized stream of air in a direction transverse to the direction of the stream of material exiting the nozzle. Upon shut off of the nozzle, the pressurized air is directed in this transverse manner to wipe off or clean the nozzle by blowing any excess or accumulated material on the nozzle back onto the just applied bead. Unfortunately, this method cannot be used in situations in which the transverse blowing action will in some way disturb the desired bead pattern in an unacceptable fashion.
Finally, U.S. Pat. No. 4,970,985 discloses a dispensing apparatus and method for reducing hot melt adhesive tailing. A plurality of air jets surrounding the discharge and of the nozzle are utilized to direct individual pressurized air streams which strike the adhesive tailing of the dispensed material to follow the desired pattern of the just applied adhesive. The prevention of drooling or dripping from the discharge end of the nozzle itself is not adequately addressed or corrected by the apparatus of U.S. Pat. No. 4,970,985. More specifically, while the "tail" of the bead may be impacted by the air streams to urge the tailing to follow the desired pattern of the applied bead, the discharge passage of the nozzle is left unaffected by the air streams. Therefore the air streams do not prevent dripping and drooling of adhesive from the discharge passage upon shut off.
It has therefore been an object of the present invention to prevent dripping and drooling of material from a dispensing head or nozzle during the shut off period of an intermittent dispensing operation which solves the above-mentioned problems in the art.
It has been another object of the present invention to provide an anti-dripping or anti-drooling nozzle which is easily adapted to operate with a wide variety of intermittent dispensing devices.
It has been a further object of the invention to provide such an anti-dripping or anti-drooling dispensing head which efficiently operates off the exhaust air of the dispenser to provide a quick and full shut off of material from the dispensing head.